I suppose this is the 21st century equivalent of TPing houses or stealing the mascot. Unfortunately for this dude it's also a felony, apparently. (Though I have to imagine they will let him plead to something lesser.)
Though, literally speaking, both of these require more cleanup than this "hack". TP-ing requires someone to clean up, and stealing the mascot requires investigation+recovery, or re-issuing.
This is e-graffiti prosecuted as cyber-war/terror/...